1. Field of Invention
This invention relates to automated blood analysis systems, and more particularly to apparatus for automatically withdrawing and testing blood.
2. Prior Art
The proper management of patients who are critically ill with respiratory or cardiovascular disorders requires frequent monitoring of various blood parameters such as oxgygen saturation, gas content and pH. While adequate oxygenation is necessary for maintenance of life, it is also important to avoid excessively high arterial PO.sub.2, particularly in new born infants, in order to prevent Retrolental Fibroplasia and possible central nervous system damage. Similarly, the duration of high oxygen concentrations must be kept to a minimum in infants to prevent possible toxic effects in the lungs. There are numerous other situations, such as in diagnosis of critical illness, monitoring a patient's condition during certain corrective procedures, and in intensive care programs wherein blood parameters must be frequently analyzed.
However, frequent manual withdrawal of blood is undesirable due to the increased opportunity for the entrance of air emboli in the blood stream, and to the attendant necessary morbidity, particularly in new born infants. Similarly, multiple usage of an indwelling catheter has heretofore nonetheless required rearrangement of external tubing to adjust between blood withdrawal and irrigation configurations, which is subject to human error and which also presents increased incidence of air emboli infusion. Some systems known to the prior art require a constant flow of blood therethrough which unnecessarily increases blood contact with foreign surfaces, which can increase the opportunity for contamination of the blood, or which may damage the blood. On the other hand, systems known to the art which discharge withdrawn blood to waste after testing thereof have utilized an excessive amount of blood which becomes particularly intolerable in the case of critically ill new born and pre-mature infants. Other systems subject the patient to a risk of electric shock due to a continuous contact existing between the patient and electric potentials within the blood testing equipment or sensors. Systems which return blood to the patient cannot be used for destructive tests (such as glucose analysis, flame photometry, etc.).
As is known, it is common to employ saline as a compatible vehicle for use in blood pumps and tubing systems of blood test units since some of its chemical properties approach that of blood. However, depending upon the characteristics of the individual patient, blood equipment and use, it is possible to infuse undue amounts of saline into the patient's blood stream, thereby resulting in a dangerous sodium buildup. Use of intravenous solutions (I.V.) which are desirable to the patient for its nutritive or other value, as a vehicle in blood systems avoids the sodium buildup problem, but, on the other hand, has a tendency to contaminate the system with respect to the blood test transducers which are used.
Some blood parameters differ markedly from saline and pure water, which are used for cleaning a system, and may concurrently require a test principle which includes a very slow process, such as diffusion across a membrane. Repetitive usage of an effective blood analysis system requires automated washout between samples. On the other hand, efficient usage of such a system, particularly with multiple blood sources, dictates that a rather rapid analysis cycle be achievable. Blood analysis units known to the art require both manual cleaning and manual calibrations between samples.
In addition, systems known to the art do not provide adequate tests for membrane leakage in gas detection tests.